The present invention relates to an improved process for the preparation of acrylic acid by the catalytic oxidation of propylene the improvement comprising conducting the process in the presence of an effective amount of hydroquinone.
In commercial processes it is important that the process be efficient and economical. This is especially important in catalytic processes and particularly in those processes employing expensive precious metal catalysts such as palladium. In general, a desirable catalytic process provides one or more of high catalyst utility, high product selectivity and low production of side products, particularly combustibles such as carbon dioxide.
The catalytic oxidation of propylene to acrylic acid is well known. See, for example, "Encylopedia of Chemical Technology", Second Edition, Kirk-Othmer, Vol. 1, pgs. 293-295 whereat the disclosed process involved the oxidation of propylene to hydroxypropionic acid using oxides of nitrogen or nitric acid as a catalyst for the reaction. Subsequent dehydration yields acrylic acid. Also see Chapter 10, e.g., pgs. 389-400, of "Propylene and its Industiral Derivatives", by E. G. Handcock, published by John Wiley, New York (1973). A detailed description of processes to produce acrylic acid is given in "Oxidation of Petrochemicals: Chemistry and Technology" by T. Dumas and W. Bulani, John Wiley & Sons, 1974. The Journal of Catalysis, Vol. 24, pgs. 173-177 (1972) shows the catalytic oxidation of olefins over metallic palladium catalysts suspended in water. Similarly, U.S. Pat. No. 3,624,147 shows a process for preparing acrylic acid by the liquid phase oxidation of propylene with molecular oxygen in the presence of water and a noble metal catalyst. U.S. Pat. No. 3,792,086 describes a process employing a catalyst composition containing phosphoric acid and palladium metal in the preparation of acrylic or methacrylic acid by the vapor phase oxidation of propylene or isobutylene, respectively. A number of U.S. patents directed to the preparation of such products are noted therein. U.S. Pat. No. 3,947,495 shows an improved catalyst composition containing a sulfur modifier. The references and patents noted in this paragraph are herein incorporated by reference.
U.S. Pat. No. 3,076,032 describes the PdCl.sub.2 /CuCl.sub.2 redox oxidation of olefins to aldehydes, ketones and carboxylic acids such as acetic acid. Propylene is oxidized in such a system predominately to acetone and propionaldehyde as shown at column 6, lines 48-49 and quinones are utilized in this system to accelerate the oxidation of the redox system.
It is among the objects of the present invention to provide an improved process for the catalytic oxidation of propylene to acrylic acid.
Other objects and advantages of the invention will be apparent from the following detailed description.